The present invention is generally related to radio transceivers and more particularly related to an improved multi-level power amplifying circuitry for use in duplex battery-operated radio transceivers.
In the prior art, the maximum power output of power amplifiers in duplex battery-operated transceivers such as those used in portable radiotelephones was primarily dictated by the magnitude of the battery voltage and the need to conserve battery energy. Since vehicular operation was often desired in fringe areas, further away from the nearest fixed station than is typical in portable applications, there was a need for higher transmit power when such a portable radio transceiver is used in a vehicle. Furthermore, since the transmit and receive signals of such transceivers are duplexed, another power amplifier preceded by demultiplexing filters and followed by multiplexing filters and a separate power control circuit was required in order to boost the output power level by means of an external vehicle battery. This overall approach to boosting the output power level of such transceivers was costly and duplicative of transceiver filters, power amplifiers, and power control circuits.